I am getting some background noise from some Roland DS-30A active monitors. I am using the monitors' analogue connection. They also have a digital connection but I am not using it. My hardware set up is a Behringer Eurorack MX2004A external analogue mixing console plugged into the line-in of an EchoAudio Mia 24/96 soundcard. I am using 1/4 inch jack plugs at the soundcard and the mixer. When the PC tower is shut down and the mixer and monitors are switched on there is no background noise. The noise only begins when the tower is booted up.
It is difficult to describe the noise. It is not a constant buzz or a constant high pitched beep. It is a little like the faint sound of crickets (and no it isn't actually crickets--I live in England and we don't have them here!). It's not a constant sound but an irregular, periodic, repetitive sound that comes and goes every few 5-10 seconds. It looks like the electronics in the tower is causing it. It is a Dell Inspiron 560 MT tower. Any thoughts about how to eliminate it would be greatly appreciated.